Advancing Hard World Achievement
Advancing Hard World90
Complete three different Classic Mode - Hard World level.On the main menu, choose ‘Classic Mode’ then select ‘Hard World’. On this difficulty, you are playing the Levels 31 through 33 of the game.
Luckily only three levels need to be played for this achievement. Enemy placement is even more than the Medium levels, so you need to be as quick as possible shooting or avoiding them; the platform section in Level 32 is like a gauntlet with enemies shooting at you from both sides. With some practice and memorization, you shall overcome.
Thanks to IBadDriverI for the video: